1. Field of the Invention
This invention relates to projection exposure method and apparatus of the step and scan type in which for example, a mask and a photosensitive substrate are scanned in synchronism with each other relative to an illuminated area of rectangular shape or arcuate shape, whereby a pattern on the mask is exposed onto the photosensitive substrate.
2. Related Background Art
When manufacturing a semiconductive element, a liquid crystal display element, a thin film magnetic head or the like by the use of the photolithography technique, use has heretofore been made of a projection exposure apparatus in which the image of a pattern formed on a photo-mask or a reticle (hereinafter generically referred to as the xe2x80x9creticlexe2x80x9d) is projected through a projection optical system onto a wafer having photoresist or the like applied thereto or a photosensitive substrate such as a glass plate. The recent tendency is toward making a chip pattern on a semiconductive element large. Accordingly, in the projection exposure apparatus, it is required to expose a pattern of a larger area (make the area larger) on the photosensitive substrate.
In order to meet such a requirement for a larger area, a projection exposure apparatus of the step and scan type has been developed in recent years. In the projection exposure apparatus of this type, each shot area on a photosensitive substrate is stepping-moved to an exposure starting position, whereafter for example, relative to a rectangular, arcuate or hexagonal illuminated area (which is called a xe2x80x9cslit-like illuminated areaxe2x80x9d), a reticle and the photosensitive substrate are scanned in synchronism with each other. Then, patterns on the reticle of larger area than the slit-like illuminated area are successively exposed onto respective shot areas.
Heretofore, in both of a projection exposure apparatus of the above-described step and scan type and an exposure apparatus of the step and repeat type which is the non-scan type, it has been usual that a focusing mechanism for a reticle pattern disposed on the object plane of a projection optical system and the exposed surface of a photosensitive substrate disposed on the image plane (imaging plane) of the projection optical system is provided only on the photosensitive substrate side. This focusing mechanism is comprised of a detecting sensor for the exposed surface of the photosensitive substrate, and a correcting mechanism for the position (focus position) and angle of inclination of the exposed surface of the photosensitive substrate in the direction of the optical axis of the projection optical system. The detecting sensor detects the focus position of the exposed surface and the inclination of the exposed surface with respect to a plane perpendicular to the optical axis. The correcting mechanism corrects the position and inclination of a stage supporting the photosensitive substrate thereon in the direction of the optical axis on the basis of the result of the detection by the detecting sensor.
However, in the projection exposure apparatus of the step and scan type, there are cases where with the scanning of the reticle, the positional relationship between the pattern on the reticle and the projection optical system varies in the direction of the optical axis of the projection optical system. Thereby, the position and inclination of the imaging plane of the projection optical system are also varied. These variations in the imaging plane result in focus deviation.
For example, suppose a 6-inch reticle as the reticle and let it be assumed that the reticle supporting surface of a reticle stage (usually the reticle has its pattern surface side vacuum-chucked and fixed) is upwardly or downwardly inclined by 1 second with respect to the scanning direction. When at this time, the 6-inch reticle is scanned from end to end, the distance between the pattern surface of the reticle and the projection optical system varies by 0.74 xcexcm. To convert this into an amount of variation in the position of the image plane, it can be multiplied by the square of the projection magnification. Supposing a reduction projection optical system having a projection magnification of xc2xd, the amount of variation in the image plane reaches 0.18 xcexcm. This amount cannot be neglected particularly when the margin of the depth of focus is small as in the exposure of a pattern of sub-micron rule by the projection optical system.
In view of the above-noted point, it is an object of the present invention to provide a projection exposure method which, when the pattern of a mask is to be projection-exposed onto a photosensitive substrate by the step and scan system, can always expose a good image onto the photosensitive substrate even if with the scanning of the mask, the positional relationship of the mask to a projection optical system varies. It is also an object of the present invention to provide a projection exposure apparatus which can carry out such a projection exposure method.
The present invention, as shown, for example, in FIGS. 1 and 2 of the accompanying drawings, is a transfer method including:
the first step of disposing a mask (R) having a pattern to be transferred formed thereon and a substrate (W) with a projection optical system PL interposed therebetween in planes substantially perpendicular to the optical axis thereof; and
the second step of adjusting the positional relationship between the image plane of the projection optical system (PL) and the substrate (W) in conformity with a variation in the positional relationship between the mask (R) and the projection optical system (PL) in the direction of the optical axis of the projection optical system (PL) so that the image plane of the projection optical system (PL) and the predetermined surface of the substrate (W) may coincide with each other while the mask (R) and the substrate (W) are moved in a predetermined direction perpendicular to the optical axis of the projection optical system (PL) in order to transfer a pattern on the mask (R) onto the substrate (W).
Also, the projection exposure apparatus of the present invention, as shown, for example, in FIGS. 1 and 2, includes:
(a) a projection optical system (PL) for projecting the image of a pattern formed on a mask (R) onto a photosensitive substrate (W);
(b) synchronous scanning means (3, 11, 14, 16, 20) for scanning the mask (R) and the photosensitive substrate (W) in synchronism with each other in a predetermined scanning direction perpendicular to the optical axis of the projection optical system (PL);
(c) a memory device (17) for storing therein information regarding a variation in the position of the image plane of the projection optical system (PL) when the mask (R) is being scanned in the scanning direction by the synchronous scanning means (3, 11, 14, 16, 20); and
(d) an adjusting device (10) for adjusting the positional relationship between the photosensitive substrate (W) and the image plane of the projection optical system (PL) on the basis of the information stored in the memory device (17) so that the image plane of the projection optical system (PL) and the predetermined surface of the photosensitive substrate (W) may coincide with each other while the mask (R) and the photosensitive substrate (W) are scanned in synchronism with each other by the synchronous scanning means (3, 11, 14, 16, 20) to thereby expose the pattern of the mask (R) onto the photosensitive substrate (W).
According to such present invention, the information regarding a variation in the positional relationship between the mask (R) and the projection optical system (PL) in the direction of the optical axis of the projection optical system (PL) while the mask (R) is moved in the predetermined direction perpendicular to the optical axis of the projection optical system (PL) is stored in the memory device (17). When the pattern on the mask (R) is to be transferred onto the substrate (W), the position and inclination of the photosensitive substrate (W) is corrected on the basis of the information stored in the memory device (17). This leads to the advantage that even when the positional relationship between the mask and the projection optical system varies during scanning, the mask pattern can be exposed onto the photosensitive substrate in a good state. Also, even if the adsorbing surface for the pattern surface of the mask (R) and the running surface of the mask stage (3) are not parallel to each other due to the manufacturing error or the like of the mask stage (3), the mask pattern can always be exposed onto the photosensitive substrate with good focus accuracy.